Physics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt.........7z&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, SAN DIEGO, 1994.Source: Dissertation Abstracts International, Volume: 55-11, Section:
Physics
Scientific paper
Theoretical analyses of the dynamics of MHD turbulence are presented in this work. Three different works are done. In the first work, the renormalization group (RNG) method is used to study the physics of two-dimensional (2-D) magnetohydrodynamic (MHD) turbulence, especially the scaling relations in k-space. We find that no RNG transformation fixed point exists on account of the coexistence of energy transfer to small scales and mean-square magnetic flux transfer to large scales. The absence of a fixed point renders RNG method incapable of describing the 2 -D MHD system. A similar conclusion is reached for 2-D hydrodynamics, where enstrophy flows to small scales and energy to large scales. These analyses suggest that the applicability of the RNG method to turbulent system is intrinsically limited, especially in the case of systems with dual-direction transfer. In the second work, the nonlinear dynamics of the magnetic shearing instability (MSI) and MHD turbulence in accretion disks in the presence of a vertical magnetic field B_0 is discussed. The saturation levels of the fluctuating fields, the angular momentum flux, the energy dissipation mechanism, the generation of an azimuthal magnetic field, and the interaction of MSI with internal waves are examined in detail. The effective Shakura-Sunyaev "alpha" value is predicted to be of order V_{A_0 }/Cs. We find that it is impossible to decouple vertical MSI saturation from azimuthal MSI evolution. Also, MSI and internal wave dynamics must be treated on an equal footing since the interaction is weak. In the third work, turbulence suppression and drag reduction by an external magnetic field in shear flows with small magnetic Reynolds number R_{m } (= l~upsilon/eta << 1) are investigated theoretically. The analysis indicates that magnetic fields induce local dissipation and alter the turbulence intensity profile. It lowers the fluctuation level and decreases the total momentum transport. It is also noticed that an anisotropy is induced due to the dependence of fluctuating energy on kz . Our results agree well with experiments on mercury pipe flows. Finally, the application of this theory to a thermal plasma jet is discussed.
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